How to change the language of an app when the user selects language using Kotlin?

This example demonstrates how to change the language of an app when the user selects language using Kotlin.

Step 1 − Create a new project in Android Studio, go to File ? New Project and fill all required details to create a new project.

Step 2 − Add the following code to res/layout/activity_main.xml.

Example

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
   android:id="@+id/rl"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:padding="10dp"
   tools:context=".MainActivity">
<TextView
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:layout_centerHorizontal="true"
   android:layout_marginTop="50dp"
   android:text="Tutorials Point"
   android:textAlignment="center"
   android:textColor="@android:color/holo_green_dark"
   android:textSize="32sp"
   android:textStyle="bold" />
<Spinner
   android:id="@+id/spinner"
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:layout_centerInParent="true" />
<TextView
   android:id="@+id/string"
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:layout_below="@id/spinner"
   android:layout_centerInParent="true"
   android:text="@string/thank_you"
   android:textColor="@android:color/holo_orange_dark"
   android:textSize="24sp"
   android:textStyle="bold" />
</RelativeLayout>

Step 3 − Add the following code to src/MainActivity.kt

import android.content.Intent
import android.os.Bundle
import android.view.View
import android.widget.AdapterView
import android.widget.AdapterView.OnItemSelectedListener
import android.widget.ArrayAdapter
import android.widget.Spinner
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import java.util.*
import kotlin.system.exitProcess
@Suppress("DEPRECATION")
class MainActivity : AppCompatActivity() {
   lateinit var spinner: Spinner
   lateinit var locale: Locale
   private var currentLanguage = "en"
   private var currentLang: String? = null
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      title = "KotlinApp"
      currentLanguage = intent.getStringExtra(currentLang).toString()
      spinner = findViewById(R.id.spinner)
      val list = ArrayList<String>()
      list.add("Select Language")
      list.add("English")
      list.add("Español")
      list.add("Français")
      list.add("Hindi")
      val adapter = ArrayAdapter(this, R.layout.support_simple_spinner_dropdown_item, list)
      adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item)
      spinner.adapter = adapter
      spinner.onItemSelectedListener = object : OnItemSelectedListener {
         override fun onItemSelected(parent: AdapterView<*>, view: View, position: Int, id: Long) {
            when (position) {
               0 -> {
               }
               1 -> setLocale("en")
               2 -> setLocale("es")
               3 -> setLocale("fr")
               4 -> setLocale("hi")
            }
         }
         override fun onNothingSelected(parent: AdapterView<*>) {}
      }
   }
   private fun setLocale(localeName: String) {
      if (localeName != currentLanguage) {
         locale = Locale(localeName)
         val res = resources
         val dm = res.displayMetrics
         val conf = res.configuration
         conf.locale = locale
         res.updateConfiguration(conf, dm)
         val refresh = Intent(
            this,
            MainActivity::class.java
         )
         refresh.putExtra(currentLang, localeName)
         startActivity(refresh)
      } else {
         Toast.makeText(
         this@MainActivity, "Language, , already, , selected)!", Toast.LENGTH_SHORT).show();
      }
   }
   override fun onBackPressed() {
      val intent = Intent(Intent.ACTION_MAIN)
      intent.addCategory(Intent.CATEGORY_HOME)
      intent.flags = Intent.FLAG_ACTIVITY_CLEAR_TOP
      startActivity(intent)
      finish()
      exitProcess(0)
   }
}

Step 4 − Create values-es, values-fr, values-hi and add the following code −

values-hi/strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
   <string name="app_name">Sample</string>
   <string name="thank_you">???????</string>
</resources>

values-es/strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
   <string name="app_name">Sample</string>
   <string name="thank_you">Gracias</string>
</resources>

values-fr/strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
   <string name="app_name">Sample</string>
   <string name="thank_you">Je vous remercie</string>
</resources>

values/strings.xml

<resources>
   <string name="app_name">Your App Name</string>
   <string name="thank_you">Thank you</string>
</resources>

Step 5 − Add the following code to androidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.q11">
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>

Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click the Run icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen